Combination reaming and burnishing tool



Feb. 2, 1960 c. GRAGE 2,923,181

COMBINATION REAMING AND BURNISHING TOOL Filed Oct. 31, 1958 2 Sheets-Sheet 1 RWWW\ Feb. 2, 1960 c. GRAGE 2,923,181

COMBINATION REAMING AND BURNISHING TOOL Filed Oct. 31, 1958 2 Sheets-Sheet 2 COMBINATION AND BURNISHING Casper Grage, Palatine, Ill., assignor to The Doall Company, Des Plaines, Ill., a corporation of Illinois Application October 31, 1958, Serial No. 771,009

' 6 Claims. 01. 77-72 This invention relates to the metal machining art, and refers more particularly to the finishing and sizing of drilled holes.

The conventional method of finishing and sizing holes by reaming may be satisfactory for ordinary work, but where very close tolerances must be met and a smooth surfaced, truly round hole is required, reaming will not suffice. .This is especially so if the holes to be finished are in the newly developed alloys which do not respond very well to machining by means of the 'bascially designed tools conventionally employed.

With a view toward improving conventionally reamed holes, the reaming operation was often followed by aburnishing operation, but heretofore, even this failed to produce a truly round axially straight hole.

The present invention overcomes the deficiencies of past methods and tools for reaming and burnishing holes and, to that end, has as its object and purpose to provide an improved method and tool for reaming and burnishing a hole in one operation.

Another object of this invention is to provide a combination reaming and burnishing tool which is extremely simple in design and construction.

A further object of this invention is to provide a combination reaming and burnishing tool, which may have its reamer portion resharpened several times and still produce holes of the intended size.

With the above and other objects in view which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

The accompanying drawings illustrate one complete example of the physical embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

Figure 1 is a perspective view of a combination reaming and burnishing tool embodying this invention;

Figure 2 is a side elevational view of the tool illustrating particularly its burnishing section and the adjacent portion of its reamer section, said view being taken on the plane of the line 2-2 in Figure 4;

Figure 3 is a view similar to Figure 2, but with the tool rotated 90 and viewing the same on the plane of the line 33 in Figure 2;

Figure 4 is a bottom end view of the tool;

Figure 5 is a cross sectional view through the burnishing section of the tool taken on the plane of the line 5-5 in Figure 2;

Figure 6 is a view at an enlarged scale illustrating how the tool is used to practice the method of this invention; and

Figure 7 is a view similar to Figure 6 but at a still larger scale and showing only a portion of the tool, to

2,923,181 Patented Feb. 2, 1960 better illustrate the difference in result accomplished by the reaming and burnishing steps.

Referring now particularly to the accompanying drawings, the numeral 5 designates generally the tool of this invention, which, as shown in Figure 6, may be used to ream and burnish the surface of a drilled hole 7 in one operation. In many respects the tool resembles a con-' ventional reamer. It has the customary shank 8 at its upper end and elongated reamer teeth 9 at its lower end. The reamer teeth 9 are formed in the usual way by flutes l0 and have the customary cutting edges 11.

Every other flute 10 extends a substantial distance beyond the upper end of the reamer teeth to define a burnishing section, indicated generally by the numeral 12. The lands between the extended portions of the flutes 10 have raised burnishing pads 13 formed integrally thereon. These pads, as best shown in the cross sectional view Figure 5 have arcuate extremely hard working faces 14 which are truly concentric to the axis. of the tool, and inclined approaches 15 leading to these working faces. The sides 16 of the pads are also inclined, but the angle of their inclination is unimportant.

A saw slot 17 extends into each of the lands between the flutes 10' from the wide trailing side of the flute, with the outer edge of the slot meeting the junction of the curved face 14 and the wide side 18 of the flute. The angle at which these saw slots are formed is such that if projected the slots would break through the adjacent narrow side of the next flute 10', and the maximum depth of these slots is sufiicient to extend beyond the lead-' ing edges of the arcuate or curved working faces of the burnishing pads. For convenience of manufacture the bottoms of the slots are arcuate.

By virtue of the saw slots 17, the burnishingpads are resiliently or yieldably maintained in their positions, the yieldability provided by the slots being an important factor in the attainment of the objectives of this invention.

In the operation of the tool its reamer section functions in the customary manner, its teeth removing metal and sizing the hole to the extent that any reamer is capable of doing so. But the reamer section or portion of the tool has an additional and very important function-it serves as a pilot and guide for the burnishing section. Because of the length of the reamer section, the tool is firmly and rigidly held exactly coaxial with the hole, and accordingly as the burnishing section enters the hole and moves helically down into it, it is held against shifting laterally so that the finished hole is straight and true. The individual pads, however, can

yield slightly to localized high spots and, in so doing, prevent the metal galling or seizing on the faces of the pads. Such yielding of the individual pads, however, does not affect the accuracy of the hole size or its straightness as would be the case if the burnishing pads were not firmly and positively guided in their motion down through the hole.

Obviously, of course, the radius of the working faces on the burnishing pads is slightly greater than that of the reamer teeth, and determines the size of the finished hole.

Inasmuch as the diameter of the finishedhole is determined by the burnishing pads, the reamer section of the tool can be resharpened several times without loss of accuracy in the size of the finished hole; To illustrate, three inch holes were drilled in a piece of SAE-2 cold rolled steel. Three one-half inch reaming and burnishing tools of this invention were selected, with the radii of the burnishing pads on each of the three tools measuring exactly alike. The reamer sections of the three tools, however, were of different diametersone was ground to minus .001, the second was 3. ground to minus .002, and the third to minus .003. Each tool was used in one of the three holes, and the three holes identified with the tools used in them. The proper speed and feedwas selected for. reamers of this type, size and the specified material, andeach hole was reamed and burnished atthe same speed and feedl 'When. all holes were thus reamed and burnished;.a plug gage and inside bore gage were used tov determine the actual size of the holes andfrom thisibwas foundthat the three holes measuredexactly alike.

Although this invention provides a new and improved tool, it also presents a newmethodof finishing holesin metal, which is quite. apart from the operation or used the tool. This aspect of. the invention resides in the cone ceptof firmly and solidly guiding the burnishing .padswas they are fed down into the hole to perform their function. Burnishing the surface of holes is. by no means new, but heretofore no effort was made to support ,the burnishi ng tool in such a way that it moved straight downthe axis ofthehole. Accordingly, with. past methods it.was not uncommon for. a burnished hole to be crooked, though .at any, given pointthe hole would havev its expected'size. With this invention the means employed. to burnishthe sides. of the hole is accurately and solidly guided, ascan be understood from Figures 6 and.7.

In addition to providing rigid guidance for the burnishing pads by pilot means moving in advance of the pads and supported by the sides of the hole,,it.is also. im. portant to the method of-this invention to have the pads resiliently oryieldably. maintained in their operative positions.

Succinctly stated, the method contemplates the steps of:

(l) Simultaneously moving a. plurality. of.circumferentially spaced hard surfaced burnishing padsv helically down through a hole;

(2) Yieldingly maintaining the. burnishing pads at a predetermined maximum radial distance from the axis of rotation as they are moved through the'hole and,

(3) Positively guiding the movement. of V the pads through the hole by supporting the same from the surface of the hole for a substantial length thereof I ahead of the areas of engagement between .thepadsand theisurface of the hole. n

With this method, the microscopically uneven surface 7' (see Figure 7) produced by a conventional reamer-'will be burnished to a smooth finishof exactly thecorrect di ameter and, in addition, the hole will be. absolutely straight throughout its length. l 7

As can be appreciated, while it is desirable that the guidance for the burnishing pads be obtained by having them part of a combination reamer and burnisher, as described hereinbefore, so that the reamerteeth serve as the pilot and support for the pads, where burnishing alone is to be done, the pads could beguided by any suitable pilot connected with the burnishing pads and having suflicient length to adequately support the pads.

From the foregoing description taken in connection with the accompanying drawings, it will be readily understood that this invention provides a greatlyimproved method of finishing drilled holes, and that. it alsopresents the industry with a valuable tool capable; of finishing drilled holes to tolerances heretofore rarely if .ever satis; fied, and that, in addition, the tool of this invention may have its cutting portion resharpened withql t affecting the diameter of the finished hole.

What is claimed as my invention is:

l. A combination 'reaming and burnishing tool comprising: a unitary stem having a fluted end portion defining elongated reamer teeth, alternate flutes extending along the stern beyond the reamer teeth; and burnishing pads on the lands between the extended portions of the flutes so as to be spaced axially from the reamer teeth and circumferentially-from one another, said burnishing pads having hard, smooth arcuate faces which collectively have an outside diameter slightly greater than that of the reamer teeth.

2. The combinationreaming and burnishing' tool of claim 1 further characterized by the fact that the burnishing pads have inclined approaches leading to their arcuate faces.

3. The combination reaming and burnishing tool of claim 1, further characterized by the provision of slots formed in .t'he lands radially-,inwardlyof the faces of the b'urnish'ing pads so that the pads are slightly yieldable radially inwardly and'are resiliently maintained in their operative positions.

4.' The combination reaming-and burnishing tool of claim 3, further characterized'by the fact that said slots extend into the lands from one face ofeach flute extens1on.-.

5. A tool for finishingthe surface of a cylindrical hole, comprising: an integral stem having a shanlc portion at one end thereof by which the tool may be gripped in a chuck; a pilot portion'at the other end of the'stem, said pilot portion having elongated circumferentially spaced guide surfaces at a uniform distance from the axis of the tool, and collectively ha-vinganoutside diameter slightly smaller than the desired diameter of the finished hole; and a plurality of circumferentially spacedburnishing pads on the stem between its shank portion and'its pilot portion, said pads having hard, smooth arcuate faces which collectively have an outside diameter exactlythat ofthe' desired diameter of the finished hole, the stem being cut away radially. inwardly of the arcuate face of each burnishing pad '50 that each pad is yieldably maintained in its normal operative position and is capable of yielding slightly inwardly during operation to prevent seizing and galling of the metalon the Working faces of the pads.

6. A combinationv reaming and burnishing tool com prising a stern made from a single piece of metal and having a shank portionat one end thereof and reamer teeth defined by longitudinal flutes at-the other end portion'thereof; and a plurality ofcircumferentially spaced burnishing pads on the stern between its shank portion and'its reamer portion, said pads .having .hard,-. smooth arcuate faces which collectively have an outside diameter slightlygreater than that of the reamer teeth, and having inclinedside approach es leading substantially tangentially from the stem tosaid'arcuate faces, the trailing sidesof thepads being formed mainly by extensions of said flutes;-

References Citedin thefile of this patent UNITED STATES PATENTS 2,039,846 Bishton Feb; 18, 1936 2,056,706' B13181; Oct. @1936 FOREIGN PATENTS 443,306 Germany 'Apr: 20, 192! 

